To satisfy or efficiently utilize the dynamic range of a backend circuit, technical personnel usually add a programmable gain amplifier (PGA) into the transmission between a signal source and a backend circuit and employ the programmable gain amplifier to selectively amplify signals with a variable magnification power to make these signals match the standard of the backend circuit or the signal standard defined by the users.
Typically, conventional programmable gain amplifiers, such as non-inverting amplifiers, are designed with one or more operational amplifiers and one or more resistors. However, programmable gain amplifiers with such a structure cannot efficiently block noises, and they amplify noises while amplifying desired signals so that the signal-to-noise ratio (SNR) in the outputs of the programmable gain amplifiers decreases.